Orientation mask for Atmospheric Dispersion Corrector (ADC) and 200mm Newtonian. by FabriceF

Last crawled date: 3 years, 1 month ago

ADCs must be aligned with the horizon as seen through the eyepiece, which is difficult with a Newtonian.
This mask should be placed in front of the aperture and orientated horizontally using the bubble level as shown in the picture (£1.50 on ebay) so it hides the bottom half of the aperture. A defocused image of a star or a planet will then look like a half-disc, showing the position of the horizon as seen through the telescope. You can then rotate the ADC accordingly. Don't forget the image is inverted!
The smaller half-disc on top is not for prettiness only: it prevents the mask from accidentally falling inside the telescope!
The diameter of this thing is 220mm, which fits nicely inside a Sky-Watcher Explorer 200P.
It can be printed on a 200mm bed if you rotate it by 45 degrees.